Posted
by
timothy
on Sunday January 30, 2011 @11:09PM
from the mind-the-gap-sir dept.

An anonymous reader writes "Molybdenite (MoS2) can be used to make transistors that consume 100,000 times less energy in standby state. This mineral, which is abundant in nature, is often used as an element in steel alloys or as an additive in lubricants. Research carried out in Switzerland at the Ecole Polytechnique Fédérale de Lausanne's Laboratory of Nanoscale Electronics and Structures (LANES) has revealed that is a very effective semiconductor. Molybdenite's 1.8 electron-volt gap is ideal for transistors and gives it an advantage over graphene (which does not have a gap)."

It's worth noting that Dow doesn't have a lock on that stuff: I have a Dri-Slide brand moly lube. Nope, definitely don't wanna let it touch skin.

Speaking of playing with arsenide chunks of stuff, I once had ore samples of arsenopyrite when I was a kid. Guess what I did with them? I heated them of course! I was 'rewarded' with a nice pretty purple vapor....

You need 99.995+% purity for most semiconductor stuff (99.999+ for CPUs and memory) which can be achieved only via zone smelting. In order to zone smelt the material needs to be able to re-crystalize after being heated locally in the first place. If it does not you can forget using it as a production semiconductor. There are in fact plenty of materials out there which have electron gaps are more "interesting" than silicon. We just have not figured out how to grow to purify them in quantity.

As far as MoS2 is concerned it does not melt and does not recrystalize (it decomposes straight away) so zone smelting is not an option. It decomposes straight away. So frankly I do not see how you can achieve 99.99+ purity to do anything useful with it.

Could we not try vapour phase deposition? I dunno, I've not looked at the numbers but I think that may help if we cannot zone refine.
Alternatively for a thin layer you could lay it down by sputtering a coat on with a mass spectrograph to precisely select the ions you wanted - slow and doesnt make a very thick layer but that seems to be a bonus from what I read..

In the latest technologies a lot of current is wasted to subthreshold conduction [wikipedia.org]. Current that flows then the transistors should be "off".

A material with a higher bandgap 1.8ev to silicons 1.1ev will naturally have less leakage. As it is an exponential thing the leakage should not just be a reduction of 1.1 to 1.8 thing but much more significant.

In insulators, there are no energy states that involve conductive electrons. In conductors, all of the energy states involve conductive electrons. In semiconductors, electrons normally reside in a nonconductive state but you can inject some energy and the electrons will be raised to a conductive state. The amount of energy required to raise the electrons to a conductive state is that semiconductor's gap.

Leakage current has been the dominant issue since the days of the P4 and the first nVidia vacuum cleaner. As the devices have gotten smaller, the leakage has gone up significantly. To combat this, they've stopped increasing clock speed and started to use a lot of clock-gating and power gating where parts of the chip are inactive or even turned off. They are at the point where a higher gate voltage to turn on should not offset the reduced power dissipation due to leakage current.

How would clock speed increase leakage current? Higher clock speed cause higher current drain, because the input capacitance gets charged at every logic transition, but leakage current shouldn't change.

Higher clock speed indirectly causes higher leakage, in that designs targeting higher frequencies require more pipe stages which require more intermediate flip-flops which means more leaking transistors. So "speed demon" designs like the P4 have been discarded in favor of more "brainiac" solutions, and leak

There's some marginal validity to that claim for bipolar transistors, but modern digital ICs make very little use of bipolars.

FETs are adjusted by doping levels to be off when no voltage is applied, and more conductive as voltage is raised (NFETs). As long as the bandgap is in a useful range so that doping can bring the device near conductivity, bigger bandgap will not increase the required voltage. (Bandgap falls with temperature, which is one fa

Molybdenum is generally gathered as a byproduct of other mining operations. The "free" molybdenum in soil that plants uses is utterly unaffected when you tear open a mountain to get at it. The original point of "OMG BUT PLANTS USE IT!" was dumb and reactionary. Hell, just re-read the original post if you are in doubt. This is like if someone declared that they found a novel use for nitrogen and someone else freaked out be cause OMFG nitrogen is critical for all life!!!11!!

There are actual legitimate road blocks to using molybdenum in place of silicon. OMFG the plants!11!!! isn't one of them.

There might not be any immediate consequences to mining molybdenum in vast quantities, but you're thinking is short-sighted. What we're talking about here tantamount to SEQUESTERING molybdenum out of the environment... where plants can't get at it through natural processes like erosion. Never heard of erosion? It may not affect plants for a millennium, but what doesn't GO around doesn't COME around. This is a finite and closed ecosystem. That was the point of the GP. We're doing the same with many ele

Yes, we are sequestering it. We are storing it so efficiently that there is no chance of it or any other material used in these circuits ever leaching back into the environment in a landfill. It is such a closed system that in a millennium there will be no molybdenum left, it will all have leaked out into these chips. And even if could seep out of these chips, everyone uses their electronics for 100 years or more, none of them are ever disposed of.

I have futures in all kinds of elements, from molybdenum to iridium....I don't think you're even close enough to having the relevant experience to be able to talk, sir. Come back when you're actually fabricating semiconductors, okay?

Because buying futures in metals is exactly the same as being a chip manufacturer....

Although unfair comment, you are the guy that claimed to need a more precise quadratic equation in order to make your LED lights for growing pot, so I'm not particularly sorry.

You are aware that we've been using moly disulphide in lubricants for a hundred years or so - I hardly think that this will cause a problem since we are already in fact mining and using the stuff. Simply taking it out of a mine, cycling it through some components that then get discarded and recycled will if anything increase the soil availability of molybdenum.

Huh? Just like all the steel we produce somehow reduces the amount of iron plants and animals can make use of? Are you suggesting that a significant fraction of mined molybdenite goes to fertilizer manufacture?

Molybdenum may not be as abundant as silicon, but it's still fairly abundant. (54th most abundant in the crust and 25th most abundant in sea water, says Wikipedia.) And given its fairly high cost, I imagine any increased demand will be offset by its cost. This would limit molybdenum to niche applications where controlling leakage is a must. I imagine MoS2 based semiconductors would only be cost effective if they can figure out how to use as little of it as possible, perhaps with MoS2 over some other substrate.

I can think of much stupider things that we could do (and in fact are doing already), such as bottling water, or hyperfocusing food production on corn and subsidizing large quantities of corn-based ethanol production.

I imagine MoS2 based semiconductors would only be cost effective if they can figure out how to use as little of it as possible, perhaps with MoS2 over some other substrate.

Near as I can tell it's dirt cheap. I figure the cost will be the same as current processors, getting it to ultra-pure quality and the etching process. You can get a kilo of not-so-very-pure MoS2 for about a buck [dhgate.com]. Even silicon good enough to make solar cells costs $67 dollars a kilo [greentechmedia.com] according to this 2009 article. The rest is for turning it from a lump of metal to a working processor.

Well, according to Wikipedia, pure molybdenum was going for $30,000 a tonne in August 2009 [wikimedia.org] and before that had shot up to $100,000 a tonne for several years. (That works out to $30 / kilo and $100 / kilo respectively.) I based my cost statement on the higher number on the basis that MoS2 semiconductors would increase the demand.

I guess that cost puts it on a par with silicon for bulk material cost. More expensive potentially, but not orders of magnitude more like I was thinking. The rest comes, as you s

The steep swing suggests that the annual production of molybdenum is fairly fixed (rather inelastic), at least for the time being. This suggests to me that you would probably have to find new mines or new extraction techniques (say from seawater?)

Ok, so I googled around and found this interesting report. [roskill.com] It seems that molybdenum production has more or less kept pace with demand. It appears that the price remained high because demand was leading supply slightly. When demand fell behind supply, the price tanked.

Recalling history, before silicon was used in transistors, what they called pure silicon had sufficient contaminants that transistors usually couldn't be made from it. They had to improve the purity by about a factor of 10 before it was good enough for single transistor chips.

I wonder just how pure molybdenum needs to be to be considered pure? I'd guess, just based on history, that the purity will need to be a *lot* higher to use in in integrated circuits. So the price estimate is probably extremely low.

Yeah, it wasn't clear to me either how they'd get the MoS2 into the transistor channels either. To build such a thin structure suggests some sort of vapor deposition process if they were to commercialize it.

Digging through a couple of the links, I finally found what this experiment did in the supplemental information PDF. [nature.com] Their current method doesn't sound like it scales to building arbitrary chips yet:

Lubricant use is pretty niche too; 80% of molybdenum is used in making steel and iron alloys. Granted, that figure includes non-MoS2 use, but electronics industry will probably start synthesis from pure Mo instead of purifying products of existing MoS2 plants.

I'll tell the mining companies to keep that in mind before they turn every atom of Molybdenum in earth's crust over to the semiconductor fabs. Also, I'll ask them not to grind up old chips and dust crops with them. We good?

Many other elements are critical trace elements, but I dont see people complaining about using nickel for things like steelmaking....
Simple stating this is dumb without telling people why doesnt help. It's been shown that Mo is used in lubricatanrs for a century or so without problems. Simply saying that a few extra kT is suddently going to cause a problem without saying why doesnt cut ice.
After all, we use a lot of moly - no issues so far. We use a lot of copper as well - another trace but that's not a

Lets totally get this ball rolling, and replace as many current devices and server farms as possible. So many people advocate cleaner energy solutions, but neglect the possibility of ridiculously increased efficiency. I say, if we can make retarded huge increases in efficiency, we can significantly reduce our power consumption. Plus, can you image a goddamn smart phone with a week long battery life?? Or a laptop that runs for days without needing to recharge? A server farm that could be powered by

You want to save energy by replacing as many of the the currently installed systems in the world? Why do I get the feeling that trashing perfectly good equipment, and manufacturing replacements is not the best use of our energy resources.

Replacing a gigawatt server farm with one that uses watts is such a substantial energy savings, that it is difficult to imagine. It would be like replacing a factory with the power usage of a lightbulb and producing just as much. This is a difference of 100,000 times less energy. That is worth it.

Most transistors are idle most of the time, and any electron gap below 1.6 eV is going to leak like a an old ladies bladder. Silicon has a gap of 1.1, allowing electrons to cross it with relative ease. Molybdenum disulfide has a gap of 1.8 eV, higher than the charge of a single electron, making it orders of magnitude more difficult to leak any power.

Think about some basic gates, like the nand, nor, not, and, xor, and, or, the different kinds of flip flops, and think about what percentage of the transistors

Well yeah, but the OP was saying to take your brand new devices and replace them immediately with this new technology. My point is what you seem to be talking about as well, that it would probably be a better use of resources to replace them when they reach EOL and not sooner.

in reality, you will just get more features out of the same die consuming the same amount of power than today. We did great with small CPU, the software we run on them just became full of bloat (not to speak about all the HD crap). That said, Intel's business is to sell you a new CPU every few years, not make it last 15 years.

That was true up to a point. Over the last 5 or so years, we hit the 'good enough' point on computers. Power efficiency is where it is at now. With the last round of upgrades in my home, I went from an average power usage of 180kw on my computers to an average of 40kw. That doesn't even include the fact that most of my computers can actually go into stand by now.

Unless we create a magic battery, power consumption will always be a huge thing for laptops and cell phones. Data centers too certainly measure performance/watt. But I agree, for the regular desktop it's no longer a big deal, if it ever was.

Yes, yes... I did mean what. I was going to put the monthly kwh usage but decided I didn't want to go through the math considering the times of use changes better computers brought and so forth. I didn't switch back to watts. Lets just chalk it up to Verizon Math, and move forward.;)

Plus, can you image a goddamn smart phone with a week long battery life?? Or a laptop that runs for days without needing to recharge? A server farm that could be powered by solar power and a few large battery power storage units?

You have misunderstood the article. It clearly says molybdenite transistors consume 100.000 times less energy than silicon ones in STANDBY. Not when operational. Sure, it would increase efficiency of mobile devices where you turn unneeded transistors off to save energy, but it would do nothing for when the system is operational and in use. Thus your idea of a server farm being solar powered is completely without basis.

Molybdenite's strength is in mobile applications: when the device is in standby mode it consumes a lot less energy than traditional silicon-based ones. But it has another strength here: silicon is a 3-layer material, whereas molybdenite is monolayer. This means that you can make smaller chips, or cram more stuff in a chip of the same size.

I toured a facility that produced micro-chips with a 70 nm process a couple years ago, it was a student facility, hence the out of date machinery, but it could successfully deposit layers of all kinds of different materials on the chip dyes with relative ease. I'm sure it won't take a few engineers more than a couple months to figure out how, and then put it into an industrial machine.

Well, many people have already addressed the flaws with your argument (such as the energy costs of manufacturing replacements for all this equipment), but more critically, you've failed to realize that this is at such an early stage of discovery that it's still highly likely to fizzle without going anywhere.

Just because you can make a few samples that perform well in a lab doesn't mean you can produce products with it in a consistent and energy-efficient manner. Just look at gallium arsenide - Two decades

Clearly you didn't read the article, and your condescending tone is not just obnoxious, it is pathetic. Come off it.

The importance of this discovery is held a lot higher than other discoveries precisely because it lacks the various problems of certain materials. First of all, it is just another layer added to silicon chips, the silicon is going to do much work that it already does. Second, it has a high voltage gap that makes it much more efficient and avoids the issues that graphene has in this area, but

Molly's Revenge [mollysrevenge.com] are one of the local Irish bands seen here in the Bay Area. (Apparently they were a follow-on to an earlier band called Dance Around Molly, but with a name like "Molly's Revenge" they eventually had to wrote a song involving someone named Molly and some revenge...)

There are plenty of materials out there that make good semiconductors, the question is: can we make them?

Moly disulfide is a material a couple of different graphene groups have been looking at (hey, we know there's an issue with graphene). What this paper really means is that the Ecole group has figured out how to *make* MoS2 better than other people, and that's really the hard part. Of course, they're still making devices using scotch tape exfoliation...

Sing it, brother! I work in compound semiconductor designing RF chips. I know a lot of silicon guys and very few of them have any clue what makes silicon a damn useful semiconductor (namely, it's oxide). I can't think of another semiconductor that has anything like as nice an oxide as silicon, easy to grow, very effective insulator with decent breakdown. If any of the compound semiconductors had anything like as good a native oxide, there would be no silicon industry (silicon otherwise mediocre electron mob

If any of the compound semiconductors had anything like as good a native oxide, there would be no silicon industry (silicon otherwise mediocre electron mobility and band-gap, though ok thermals).

I don't know about that... most compound semiconductors have really good electron mobility and so-so or worse hole mobility. One of silicon's great strengths is that the hole mobility is only 3X smaller than the mobility for electrons so p-channel devices are useful.

I think it's because hole mobility in silicon isn't dreadful that p-channel devices are used. You don't actually need them to make logic. The Cray supercomputer was done with GaAs MESFETs, for instance. Logic is GaAs FETs is very fast, with depletion mode and enhancement mode devices working pretty well together to make any sort of gate you want. But off-state leakage limits gate density to much much less than can be achieved with silicon (it's not a lithographic limit - 20nm style gates are possible in GaA

This mineral, which is abundant in nature, is often used as an element in steel alloys or as an additive in lubricants.
That is a joke, isn't it? Or is it just/.?
From Wikipedia:
Molybdenum is the 54th most abundant element in the Earth's crust and the 25th most abundant element in the oceans, with an average of 10 parts per billion; it is the 42nd most abundant element in the Universe.
That is not abundant that is pretty rare. Considering 35% of the planet is silicon... or is it more?
Regards,
Angel

How much of that silicon is ultra pure semiconductor grade? Probably none, so both materials need to go through a refining process. If there are areas with high moly concentrations, it doesn't matter how much the rest of the world has, as long as those mines are enough to meet demand (and can continue to do so for a while).

You don't need 10kg of the stuff to make a semiconductor device. Compare it to gold: we produce about 30x more Mo, and you certainly have a few grams of gold somewhere in your house. Anyway my guess is that it might be laid down in layers on top of an insulating substrate (and the substrate doesn't have to be MoS2). So the quantities required are not out of line with production, despite the fact that it is relatively rare in the universe.

From the same wikipedia page - a kilogram of molybdenum costs about 30$, so it's just as abundant as dirt for any practical chip production purposes.

42nd most abundant element in the universe means that it's about average, as about half elements are rarer. You could call it rare if it was a couple orders of magnitude less abundant, such as gold, palladium or others.

Guess what's a popular use of that rare element gold? Electronics is a common use for gold. So if we can afford to use gold, you're saying molybdenite should be not only not a problem, but really makes no sense not to use it for this kind of energy savings.

let me know when you have I-V curves for a moly disulpide FET. Both p and n types please.

I learned many moons ago, that one of the most important things about Si is the fact that it's so easy to grow an oxide. It's EXTREMELY useful when processing integrated circuits. Otherwise everything electronic would use III-V's.

Any new material which aims to replace Si is going to need an equivalent process capability.

Personally I'm hoping for a breakthrough in organic semiconductors. I want to be able to screen print transistors at home.

I don't see moly transistors replacing the entirety of silicon transistor applications in the same way that graphene will never replace silicon.

I can, however, see moly transistors stepping in for the power regulation side of a chip and system where efficiency is demanded, and graphene-based 'burst processing' cores that are shut down completely when not in use on the performance side.

Everything is about application, adaptation, and integration of technologies, not seeking out a replacement for every e

It is not a quirk of mathematics. It is a quirk of language.While it can be parsed the way you say, most would parse it to mean "1/100000 of previous consumption".It might not be the "right" way, but it is the way most people read it.

So on one hand what you state is correct from a mathematical standpoint but on the other hand irrelevant.It is technically incorrect but the phrase "xxx times less" has become the way people express that something is 1/xxx of what it used to be.You can yell at people until you'

More and less are opposites, so is multiplication and division. Most people take ten times more to mean x * 10 and ten times less x / 10. Neither is mathematically correct, but it has a certain logical consistency.